The predecessor in interest of the assignee of this application, Multifastener Corporation, first invented self-attaching fasteners over 50 years ago. As used herein, the term self-attaching fastener includes male and female self-piercing and self-clinching fasteners which are permanently attached to a panel, including pierce and clinch nuts. studs, bolts and the like, and pierce and clinch nuts and other female fasteners of this type. Self-attaching fasteners include a fastener portion, such as a threaded or unthreaded shank portion in the case of male fasteners, or a threaded or unthreaded bore in the case of female fasteners. In a typical application, self-attaching fasteners are fed to an installation head generally located in the upper die shoe or die platen of a die press and a die member or die button is located in the lower die shoe or die platen. The installation head typically includes a plunger which reciprocates through a plunger passage during installation to permanently install a self-attaching fastener in a panel supported on the die button with each stroke of the press. As will be understood by those skilled in this art, however, this arrangement may be reversed and self-attaching fasteners may be installed in any type of press.
Self-attaching fasteners of the type disclosed herein were first disclosed in U.S. Pat. No. 4,543,701 assigned to the predecessor in interest of the assignee of this application, the disclosure of which is incorporated herein by reference. Self-attaching fasteners of this type include a fastener portion and a tubular barrel portion having an open free end which is driven through an opening in the panel and deformed radially outwardly and accurately by a die button having a concave arcuate annular surface to permanently attach the fastener to the panel. In the embodiment of the self-attaching fastener and panel assembly and method of installation disclosed in this patent, the free open end of the tubular barrel portion is deformed radially outwardly into an L-shape and the panel is entrapped between a radial flange of the self-attaching fastener and the L-shaped barrel portion. However, this fastener and panel assembly did not provide sufficient integrity for commercial applications. U.S. Pat. No. 4,915,558, also assigned to a predecessor in interest of the assignee of this application, the disclosure of which is incorporated herein, discloses an improved method of installation, assembly and die member, wherein the free open end of the tubular barrel portion is deformed radially and accurately upwardly into a U-shaped annular channel or inverted and the panel surrounding the opening is deformed into the annular channel-shaped barrel portion to permanently attach the self-attaching fastener to the panel. The die button disclosed in this patent includes a central die post and an annular concave hemispherical die surface which receives the free end of the tubular barrel portion and deforms the barrel portion into an annular U-shaped channel. Simultaneously, the panel portion surrounding the panel opening is driven into the developing channel-shaped barrel portion forming a very secure installation. The embodiment of the self-attaching fastener and panel assembly disclosed in this patent has been and continues to be commercially successful.
There are, however, problems associated with the method of installation disclosed in the above-referenced U.S. Pat. No. 4,915,558. First, the tubular barrel portion is subject to cracking as the barrel portion is deformed against the annular concave hemispherical die surface, particularly if the roll over diameter exceeds a certain size. As will be understood, the barrel portion is subject to significant frictional resistance and hoop-stress as the barrel portion is deformed against the annular hemispherical die surface and deformed into the annular concave hemispherical shape. To reduce the frictional resistance, the barrel portion is coated with a lubricant, increasing the cost. Further, the complex die buttons are relatively expensive to manufacture and subject to failure because of the configuration of the annular concave hemispherical die surface which must be polished to minimize friction between the barrel and the self-attaching fastener and the dimensions are critical to proper installation. It is also important to note that many applications of self-attaching fasteners do not require piercing an opening in the panel with the free end of the barrel portion. Instead, an opening in the panel is prepierced or prepunched, the tubular barrel portion is received through the preformed opening and clinched to the panel as disclosed in the above-referenced patent.
The method of installing a self-attaching fastener of this invention substantially eliminates cracking of the barrel of the fastener and panel assembly, reduces the cost of the fastener by eliminating the requirement for a lubricant on the barrel and significantly reduces the cost and increases the life of the die button which is less expensive, simple and rugged in design.